Transient growth bands in silicon nitride cooled in rare-earth-based glass

Silicon nitride (Si3N4) particles embedded in various R-Si-Al-O-N
glasses (R = La, Nd, Gd, Yb) have been systematically studied by
high-resolution transmission electron microscopy and by analytical
electron microscopy. The particles typically show an internal growth
band, which is attributed to the enhanced growth of the particles in
the supersaturated silicate liquid during cooling and reheating. The
electron energy-loss spectroscopy and energy-dispersive X-ray
spectroscopy analysis reveal that the growth band typically contains
lanthanide elements. This trapping, especially of the lighter
lanthanide elements, within the lattice of the beta-SiAlON is obviously
beyond the general expectation that the lighter lanthanide ions hardly
form solid solutions with either alpha- or beta-Si3N4. This ultimately
provides some clues regarding the mobility of the lanthanide ions in
the liquids and also revives interest in the general question of the
possible effect of a cooling stage on the structures and compositions
of the intergranular film and of the grain/glass interface in the
Si3N4-based polycrystalline ceramics.